722 
from Spiddal, it would be classed as a diabase, and, accepting Allport’s view that diabase 
is really an altered condition of dolorite, it would be placed amongst the diabases, 
following after the dolerites. (Prnfessor Wadsworth places melaphyr, diabase, gabbro, 
and many of the diorites under this head, so it may remain here.)* 
Scctim . — Much augite in small grains, craL-kod ; little olivine, porpbyritic augite; 
and exquisitely clear pellucid plagiochiso felspar.s, showing several lamellae. The angle 
between the extinctions of the lamellae, right and left, is about 30°. 
Nos. 51, 52, 53, 60, and Gt. The Burdekin Eiver (Queensland). 
A. "W. Clarke’s Collection. 
No. 266. Mount Eazoeback, Utter Buedekin (Queensland). 
A. Gibb Maitland’s Collection. 
No. 267. Mount Land, Uttee Buedekin (Queensland). 
A. Gibb Maitland’s Collection. 
Sp. Gr. of No. 266, 2-667; of No. 267, 2-477. 
The first four rocks are from three well-known points on the Burdekin Eiver — 
viz., the “Top Eocks,” the “Lower Eocks,” and the Crossing at Great Sandy Creek. 
They are all vesicular black basalts. 
The weathered rocks are often found with a white secretion in the vesicles, 
probably zeolites. f 
Sc.oiion . — The ground-mass is made up of large plagioclase laths, '001 inch by 
-02 inch, mostly stepped, and polarizittg iti high colour.s for felspars, and some doubtful 
sanidine. The walls of the vesicles are lined with glass, in which occur a few very 
minute speck.s, faintly luminous, but otherwise there is little glass and no fluxion- 
structure. Magnetite in fine grains, plentiful. Augite in very small grains and 
plentiful. The porphyritic minerals are olivine and augite. Along the cracks and 
fissures of the former is a secretion of ferrite. The augite inclusions are glassy, with 
fixed bubbles, and magnetite. 
Unfortunately, the thickest section was that from which Plate 66, Big. 2, was 
drawn, so that the slice is too opaque, and in those crystals which do allow the light to 
pass the colours are too high. However, in the drawing the olivines come out very well. 
No. 266 differs from the preceding in the development of the transparent 
hydrated oxide of iron which incysts some of the olivine, so that hyalosiderite or 
fayalite must be reckoned amongst the varieties of olivine present in the rock. Certainly 
a few sanidines exist, and a little glass occurs. The rest of the rock may be described 
in the terms of the preceding note on Nos. 51, 52, 53, 60, and 64. 
In No. 267, the last of the Burdekin series of basalts, some beautiful prismatic 
felspars occur -05 inch by '002 inch, the angle of extinction with the edge of the pellucid 
crystals being 0° or 3° and 4°. Otherwise the same description applies as to No. 266. 
No. 72. Okenden, Mackay (Queensland). 
A. Gibb Maitland’s Collection. Sp. Gr. 2 704. 
A black, fine-grained, compact rock, with greyish- white streak. 
Section. — Microgranitic, graiiulitie. Plentiful magnetite. Some highly-coloured 
specks between crossed nicols, pointing to augite. No glass in the ground-mass, and 
no porphyritic constituents whatever. 
■“■M. E. Wadsworth. Preliminary Description of the Peridotytes, Diabases, and Andesytes of 
Minnesota, 1887. 
t Black ants build their nests in the vesicular cavities of this basalt. 
